1. Field of the Invention
The invention relates to height control valves in vehicle suspensions and, more particularly, to a height control valve with a mechanism for adjusting the height of the suspension.
2. State of the Prior Art
Air suspension systems have become increasingly popular for use in vehicle suspensions, seats, and cabs on semitrailer truck rigs and other vehicles. Most typically employ a height control valve which maintains the design height of the suspension. In a semitrailer suspension, for example, the design height is the spacing between the frame and the axle. The height control valve senses spacing greater or less than the design height and, accordingly, adjusts the pressure in the air springs disposed between the frame and axle to maintain the height at a controlled value. The air suspension system with a height control valve maintains a uniform height of the air spring over a range of vehicle loading conditions.
The height control valve operates by selectively admitting air into, or exhausting air from, an air spring. The air spring is positioned between the truck frame and a trailing arm. The trailing arm carries the axle so that adjusting the air spring pressure also adjusts the distance between the truck frame and the axle. The height control valve typically mounts on the truck frame and has a control arm which connects to the trailing arm through a linkage. As the distance between the truck frame and trailing arm varies, the linkage causes the control arm to rotate a control shaft inside of the height control valve, which, in turn, selectively permits air to be admitted to or exhausted from the air spring.
Typically, the height control valve has three ports: an air spring port connected to the air spring, an inlet port connected to a source of pressurized air, and an exhaust port open to the atmosphere. To increase the height of the air spring, the height control valve opens fluid communication between the air spring port and the inlet port, allowing air to flow from the pressurized air source, through the height control valve and into the air spring. To decrease the height of the air spring, the height control valve opens fluid communication between the air spring port and the exhaust port, allowing air to flow out of the air spring through the height control valve, and to atmosphere through the exhaust port. When the air spring is at the proper height, the valve is in a neutral position wherein neither the inlet nor exhaust port communicates with the air spring.
Occasionally, a vehicle operator desires to adjust the neutral position of the height control valve, thus changing the design height of the controlled portion of the vehicle. European standards require a system for manually adjusting the neutral position of the height control valve so that the vehicle can be manually raised or lowered by the introduction of air to the air spring or exhaustion of air from the air spring. A complicated add-on mechanism is connected to the height control valve to perform such functions and comply with the European standards.
An alternative solution is disclosed in U.S. Pat. No. 2,959,426 to Augustin, issued Nov. 8, 1960, which discloses a height control valve having two neutral positions. The basic operation of the valve is similar to commonly available height control valves. Air pressure at the inlet port, assisted by a small return spring, biases a disc valve against an annular valve seat to isolate the inlet port from the valve chamber. The valve chamber fluidly communicates with the air spring, and receives a tubular hollow plunger. One end of the hollow plunger fluidly communicates with the exhaust port. In the neutral position of the valve, the opposite end of the hollow plunger abuts the disc valve. Thus, in the neutral position, the air spring is isolated from the inlet port by the disc valve and from the exhaust port by the sealing abutment of the plunger with the disc valve. Axial movement of the plunger towards the disc valve moves the disc valve away from the valve seat, placing the inlet port into fluid communication with the air spring, and causing air to flow into the air spring through the inlet port. Axial movement of the hollow plunger away from the valve seat places the air spring into fluid communication with the exhaust port through the hollow actuator rod, exhausting air from the air spring.
Typically, a linkage connects the vehicle frame to the vehicle axle such that variations in the height therebetween are translated into angular rotation of a control arm on the height control valve. Angular rotation of the control arm translates into angular rotation of a control cylinder having a pin eccentrically mounted at one end. This pin is received within a groove in the hollow plunger such that angular rotation of the control cylinder is translated into axial movement of the plunger, providing feedback to the control valve for adjusting the height of the air spring. Typically, the groove is narrowly sized to accommodate the pin.
In the Augustin patent, the groove is disclosed as being considerably wider than the pin, and a spring biases one face of the groove against the pin. Upon the selective application of pressurized air to a control port, the opposite face of the groove is biased against the pin. Thus, the height control valve is provided with two neutral positions with respect to a given angular position of the control rod, depending upon which face of the groove is biased against the pin. While this design does provide an additional neutral position, thus an additional control height at which the vehicle can be operated, it makes no provision for variable adjustment of the other neutral positions between these two predetermined neutral positions.